The European Space Agency’s (ESA) XMM-Newton space observatory has captured the first X-ray images of the interstellar comet 3I/ATLAS. This groundbreaking discovery reveals a striking crimson glow in the vastness of space, offering scientists a unique opportunity to analyze the chemical composition of a celestial object from another star system. 3I/ATLAS is only the third confirmed interstellar visitor to our solar system, following 1I/’Oumuamua in 2017 and 2I/Borisov in 2019.
The comet is expected to make its closest approach to Earth on December 19, 2023, passing at a distance of approximately 270 million kilometres (about 168 million miles), nearly double the distance between Earth and the Sun. Scientists confirm that 3I/ATLAS poses no threat to our planet.
During a 20-hour observation session on December 3, the XMM-Newton detected the comet’s bright red hue, which signifies actual X-ray emissions. This phenomenon occurs through a process known as solar wind charge exchange. As the comet approaches the Sun, gas molecules escape from its icy nucleus. These molecules collide with the solar wind, a continuous stream of charged particles emitted by the Sun. When oxygen ions from the solar wind interact with the neutral gas molecules, they capture electrons, enter an excited state, and ultimately release X-ray photons as they stabilize.
The XMM-Newton‘s European Photon Imaging Camera was crucial in capturing this event. The images produced utilize color to indicate energy levels: red represents low-energy X-rays generated by the collisions, while blue highlights empty space. While other instruments such as the James Webb Space Telescope and NASA’s SPHEREx mission have already detected water vapor, carbon dioxide, and carbon monoxide, X-ray telescopes reveal gases that are typically invisible in optical and ultraviolet light.
Notably, hydrogen and nitrogen, which do not show clearly through other methods, become detectable when X-rays are involved. This is particularly significant since 3I/ATLAS formed around a different star, providing insight into the materials that make up interstellar objects. The X-ray data may also help validate a theory suggesting that 1I/’Oumuamua might have been composed of exotic ices, such as solid nitrogen or hydrogen.
Japan’s XRISM spacecraft also observed 3I/ATLAS in X-rays between November 26 and November 28, detecting a faint glow extending approximately 400,000 kilometres around the comet. The combined data from XMM-Newton and XRISM provides the most comprehensive analysis to date of how an interstellar comet interacts with the Sun’s environment. Research published in The Astrophysical Journal emphasizes that X-ray observatories can yield cometary data that is unattainable through other means.
As 3I/ATLAS approaches its closest point to Earth, the window for observation will begin to close. After December 19, the comet will continue on its path, gradually fading and becoming increasingly difficult to observe until it exits our solar system completely. This inevitable departure has prompted a significant collaborative effort involving observatories globally, all eager to gather as much data as possible.
The data collection includes X-ray, ultraviolet, optical, infrared, and radio information. Such interstellar objects are invaluable in providing samples of material from distant star systems, which we may never reach otherwise.
As scientists analyze the incoming data, they are piecing together an unprecedented understanding of what interstellar comets are made of and how they behave. This knowledge has the potential to reshape our comprehension of planetary formation, not just within our solar system but throughout the universe.
